Masato Ara

Nanopatterning of alkyl monolayers covalently bound to Si(111) with an atomic force microscope

Alkyl monolayers covalently bound to silicon were prepared through the reaction between 1-alkene molecules and hydrogen-terminated Si. The surfaces were anodized in nanometer scale with a contact-mode atomic force microscope (AFM) by applying positive bias voltage to the surface with respect to a conducting cantilever under ambient conditions. Following the anodization, patterned areas were selectively modified by chemical etching and coating with different molecules. The alkyl monolayers showed high resistance against chemical etching and protected Si surfaces from oxidation. AFM lithography of monolayers on Si was found to be useful for nanofabrication of organic/inorganic interfaces based on the Si–C covalent bond.

Atomic force microscope anodization of Si(111) covered with alkyl monolayers

Alkyl monolayers on Si were prepared through the reaction between 1-alkenes and hydrogen-terminated Si by heat treatment. The monolayers were characterized by atomic force microscopy (AFM), force curve and water contact angle measurements. It was found that surface properties were modified by the formation of highly ordered closely packed monolayers. The monolayers were anodized with a contact-mode AFM by applying voltage between the conductive cantilever and surface under ambient conditions, which resulted in nanometer-scale oxidation of surfaces. After anodization, patterned areas were modified by removing the silicon oxide and terminating the surface of the grooves with hydrogen atoms by NH4F etching, and by covering the etched surface with 1-octadecene molecules. The monolayers themselves showed high resistance to NH4F etching and air oxidation. AFM lithography of monolayers anchored covalently on Si was found to be useful for nanofabrication of organic/inorganic interfaces based on Si–C covalent bonds.

Friction force microscopy using silicon cantilevers covered with organic monolayers via silicon–carbon covalent bonds

Cantilevers covered with hydrocarbon (CH) and fluorocarbon (CF) monolayers via Si–C covalent bonds were prepared and used for adhesion force measurements and friction force microscopy of the surface patterned also with CH and CF areas. The adhesion and friction forces on CF areas were larger than those on CH areas, especially using CF cantilevers. Large polarizabilities of CF molecules compared to CH molecules are found to enhance the contrast in adhesion and friction images. The cantilevers covered with organic monolayers via covalent bonds are useful for chemical force microscopy with contact and noncontact mode atomic force microscopy in various atmospheres since the interface between molecules and cantilevers is thermally and chemically stable.

Novel SiO2-deposited CaF2 substrate for vibrational sum-frequency generation (SFG) measurements of chemisorbed monolayers in an aqueous environment.

A novel SiO2-deposited CaF2 (SiO2/CaF2) substrate for measuring vibrational sum-frequency generation (SFG) spectra of silane-based chemisorbed monolayers in aqueous media has been developed. The substrate is suitable for silanization and transparent over a broad range of the infrared (IR) probe. The present work demonstrates the practical application of the SiO2/CaF2 substrate and, to our knowledge, the first SFG spectrum at the solid/water interface of a silanized monolayer observed over the IR fingerprint region (1780–1400 cm−1) using a back-side probing geometry. This new substrate can be very useful for SFG studies of various chemisorbed organic molecules, particularly biological compounds, in aqueous environments.

Non-contact atomic force microscopy using silicon cantilevers covered with organic monolayers via silicon–carbon covalent bonds

Silicon cantilevers covered with dodecyl monolayers anchored via silicon–carbon covalent bonds were prepared by a wet process and used for non-contact atomic force microscopy (NC-AFM) of TiO2(110)-(1 × 1) surfaces. Clear images of atomic rows on atomically flat terraces were observed with the dodecyl-coated samples when they were biased around 2.0 V with respect to the cantilevers. The bias voltage required to give clear images for alkyl-coated cantilevers was higher than that for uncoated ones. Since the cantilevers are thermally and chemically stable, they are applicable to various force microscopy to distinguish chemical species on surfaces.

Effective Method for Micro-Patterning Arene-Terminated Monolayers on a Si(111) Electrode

Microstructured electrodes are significant to modern electrochemistry. A representative aromatic group, 4-ferrocenylphenyl one, was covalently bound to a micropatterned silicon electrode via the arylation of a hydrogen-terminated silicon(111) surface formed selectively on a Si wafer. Starting from a silicon(100)-on-insulator (SOI) wafer, the aromatic monolayer was attached sequentially by spin-coating a resist, electron beam lithography, Cr/Au deposition, lift-off, anisotropic etching with aqueous KOH solution, and Pd-catalyzed arylation. Cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) are used to characterize the coupling reaction between 4-ferrocenyl group and silicon substrate, and to confirm performance of the final modified microsized electrode. These data show that this synthetic protocol gives chemically well-defined and robust functionalized monolayers on a silicon semiconducting surface with a small electrode.

Preparation of Nanogap Electrodes of Silicon by Chemical Etching

We have prepared nanogap electrodes of silicon by chemical etching. The substrate used was silicon(001)-on-insulator (SOI). A metal film used as an etching mask was fabricated on SOI by a conventionally lithographic process. The direction of the mask patterns with respect to the crystal axes of silicon is a key factor for anisotropic chemical etching. The substrate was, then, immersed in a KOH aqueous solution to etch the (001) plane selectively, which resulted in the formation of the electrodes with the shape of square pyramid.

Hydrothermal Synthesis of Silicon-Based Hollow Nanostructures

Silicon-based hollow structures with a diameter on the order of 300 nm were prepared from silicon monoxide by hydrothermal synthesis without any catalytic materials. Structural analysis of the products revealed that the shell of hollow structures was composed of amorphous SiOx. It was expected that nanoscale bubbles act as cores on which thin SiOx shells grew. Since the nanobubbles are generated in water under high pressure at the nuclei formation stage, the dimension of capsules can be controlled by adjusting the pressure.

Nanocommunication Design in Graduate-Level Education and Research Training

In order to teach the accumulated knowledge of nanoscience, nanoengineering and nanotechnology to graduate school students and young scientists with the sense of public engagement, Osaka University started from 2004 to prepare and offer various kinds of education and training programs such as trans-disciplinary graduate-school minor program, evening course refresher program, short-term international research training program, etc. It offers a series of lectures, partly broadcasted live to satellite classrooms. In addition, the students can join intensive hands-on training programs using modern facilities, allowing them to design, fabricate, measure, characterize and functionalize nanomaterials and nanodevices. In addition, there are four specially designed lectures and research training programs aimed for nanocommunication including social, legal and ethical relationship: “Nanotechnology Career-up Lectures”, “Social Engagement on Nanotechnology”, “Road Map Design on Nanotechnology”, and “Project- Aimed Learning and Training Programs (PAL)”. The outline of the whole programs is described together with the specialized programs for nanocommunication.

Advanced Inter-/Multi-Disciplinary Graduate-Level Programs for Education, Research, and Training in Nanoscience and Nanotechnology Offered at Osaka University

Nanoscience: an area that promises new understanding of nature with the aid of rapid progress of nanotechnology. Nanotechnology: the use of nanoscience to build new technologies that will change the world. Nanoscience and Nanotechnology have captured the attention of the public, government, and corporations. How they will influence our lives depend on how we prepare ourselves, and our successors. Here we present a brief outline of the efforts being taken at Osaka University since 2004, in order to prepare our future scientists, engineers, and leaders in the rapidly flourishing trans-/multi-disciplinary field of Nanoscience and Nanotechnology.